Lowering intraocular pressure in Primary Open Angle Glaucoma, the most prevalent form of glaucoma, is a major objective in the treatment to prevent the progression of this ocular disease. Our long-term goal is the understanding at the cell and molecular level of the mechanisms involved in the regulation of intraocular pressure. A great body of evidence emerging, for the most part, from studies on molecular biology has supported that the human ciliary epithelium is neuroendocrine and expresses a functional peptidergic system. Many of the peptides identified are vasoactive and they are involved in the regulation of blood pressure in the cardiovascular system. The existence of a peptidergic system in the ciliary epithelium provides suggestive evidence for its involvement in the regulation of eye pressure at a "local" level by autocrine/paracrine mechanisms. In this application, we propose a 5-year study to examine the hypothesis that intraocular pressure is a neuroendocrine function of the ciliary epithelium, mediated by the expression of regulatory peptides and hormones entrained in a circadian rhythm by a non-visual light-sensing mechanism. The plan comprises three main aims. Aim 1, biochemical characterization, by HPLC and mass spectrometry, of neuroendocnne regulatory peptides with hypertensive/hypotensive activities expressed in the ciliary epithelium, including neuropeptide Y and natriuretic peptide-C. To study their signaling pathway upon activation of their cognate receptors by measuring second messengers including cAMP, cGMP and Ca2+. Aim 2, to examine the circadian variations of neuropeptides in experimental animals and cultured cell models of the ciliary epithelium entrained to light/dark cycles. To identify the components of the endogenous "circadian oscillator" that underlie the circadian gene expression in the ciliary epithelium, including melatonin-rhythm-generating enzymes and clock genes. Aim 3, to establish the molecular nature of the non-visual phototransduction cascade in the ciliary epithelium, by focusing on the expression of rhodopsin and other opsin-like molecules, and components of the activation and deactivation of rhodopsin, including rhodopsin kinase, recoverin and arrestin. To determine any light-sensing responses in intact and cultured ciliary epithelial cells, by studying the cGMP-gated channel under light and dark conditions.